Step 10: Things That Will Go Wrong

Step 11: TLDR: What Not To Do

Don't drop the bits. They will break. Don't crash the tool. I know you're going to crash the tool because you don't know what you're doing, s...

Traditionally, there are two ways of hobbyists making custom PCBs: 1. Using toner transfer and chemical etchant -- can be tricky to get the right materials, and the chemicals are nasty and messy 2. Paying a service like BatchPCB or OshPark -- fairly inexpensive, but usually have to wait a long time, like two or three weeks.

Milling them on a CNC is a quick way with a different set of pros and cons:

The good: * Quick turnaround - don't have to wait days or weeks for it to ship * The mill does the drilling * No messy acid to deal with * Once you have good settings, the process is easily repeatable * Two sided boards are possibly slightly easier than with etched boards * Inexpensive - you're just paying for blank circuit boards which are a couple bucks each

The not so good: * Bits and end mills can be expensive and they wear out. * Bits of copper clad fiberglass get all over the place * Milling a board can take a while * Board stock and mill bed flatness will present a challenge * Isolation size is a function of bit size and mill accuracy. Check your design carefully before you plan on using fancy SMT parts with densely packed pins.

How I've Made Things Work: I'm a CNC newb and an electrical engineering disaster so my milling process and the following outline use what I've determined to be the most common (though not necessarily the best) tools.

The only tricky part is related to the V shaped bit. Obviously, you will want to etch the smallest, cleanest line that you can in order to mount all of those tiny surface mount LEDs that you already bought. Unfortunately, the V shape of the bit will change the width of your cut depending on how deep you cut into the board. Since your copper clad stock isn't perfectly flat you are challenged to pick a milling depth that will cut clean traces across the entire board.

I've had some success with flattening my copper clad as much as I can by using a metal straight edge to check flatness and then bending the board by hand to try to make it flatter. With the board then as close to flat as I can make it, I would then test at what depth I can cleanly etch a line on all four areas of the board that surround the area that I plan to etch. The results were always usable but I sometimes found myself rebuilding missing traces with bits of jumper wire.

A better way seems to be to use some G-Code trickery to probe the height of the board at key points on the surface and then perturb the height of the vertices accordingly while milling. It sounds both awesome and complicated but luckily for you there is already a program that does all of the work so you can just deal with the awesome part and follow along with my directions.

I had some issues with scaling when i first started. I found that the solution to my problem was the units used in Eagle(pcb software) did not match the units I used in mach3(cnc software). Both must be in mm or inches, else it does not scale properly.

It will mirror the bottom layer so when you are etching from the top, it is flipped from what you would see in eagle. For one sided boards, what I have been doing is only using the bottom layer in eagle, so when I etch the copper, I then flip the board upside down (so now you are looking at the non-copper side) and put my parts in that way. This way it matches what you would see in eagle from a part outline perspective. Now if only there was a way to get a silkscreen onto the non-copper side based on the eagle silkscreen layers, that would be awesome!

Just wanted to comment on the cutting out of the board. By default the pcb-gcode will not generate correct milling files (will likely be empty), even if you select "generate mills" because it only understands the eagle 'milling' layer, and by default your board outline is probably on the 'dimensions' layer. What I found is if I temporarily change the board outline lines to be on the milling layer, then generate the files with pcb-gcode, I get a nice milling gcode file. Use the eagle change layer tool to do this, or select each outline and manually change it to the milling layer.

I also had to change the milling depth as by default it looked to be using the etching depth. So I set it to the same depth as my drills, such as -1.7mm and it came out great!

Hey man, great tutorial! I am doing exactly what you have done, but I am stuck on the pcb-probe part. I was wondering if I could get you to tell me how you got it to work. I tried the pre-compiled windows program, but it always tell me that I'm missing .dll files. When I get them, it still gives me an error. Without the compiler, I don't know what to do with the source code. Any thoughts or advice would be greatly appreciated.

Thanks for the reply! I didn't run a command. I just double clicked on the executable (on the pre-compiled windows version) and that's where I got the error. How do you compile it if you don't mind my asking? I'm sure that is what I need to do as well. I don't remember the error that I got. I will have to re-run it and then hunt for the .dll files again. I will do that shortly and report back.

I just uploaded a new version compiled staticly, so in theory it shouldn't need any DLLs. Download from the same place.

There is no gui, so you cannot just click on it. You need to run it from the commandline, sorry. When run it will tell you the arguments it takes.

I compiled it with mingw32, only thing I had to change was "gcc" to "g++" in the makefile. Setting up mingw32 and compiling code is a whole nother tutorial on it's own, too much to explain in a little instructables comment.

My friend works at a shop that makes CNC bits for a large aerospace company. And they scrap a lot of these bits that are imperfect (off by 0.00001 of an inch) he gives me for use with my Dremmel tool. Otherwise they get thrown in a bucket to throw away. If I buy or make a bench top CNC; am I really going to be able to mill PCB boards without going to engineering school to use it? Is it realistic to say that I can successfully design my circuits (this I can do) and work a program that will cut my prototypes? I am a minor technician at best. And I have no idea how a CNC machine interfaces with a computer. I can put together any kind of kit, But how much training and failure will I experience before I can expect to have a successful milling job? Money I have, but time to learning this device? i dunno. I have had no luck whatsoever with chemicals. But have been able to successfully use my Dremmel with these micro bits and make my own PCB boards. I have a very steady hand, and a headpiece with magnifying lense pieces. Like a jewler uses. Do you have any advice? I just dont want to spend $800, then end up selling it because I have no clue how to use it. What about cost of software? Any help would be, umm,,, helpful :)